1. Field of the Invention
This invention relates generally to nuclear reactors, and more particularly to determining a reactor core design for the reactor.
2. Related Art
A core of a nuclear reactor such as boiling water reactor (BWR) or pressurized water reactor (PWR) has several hundred individual fuel bundles (fuel assemblies) of fuel rods (BWR) or groups of fuel rods (PWR) that have different characteristics. These bundles (fuel rod groups) are preferably arranged so that interaction between rods within a fuel bundle (rod group), and between fuel bundles (fuel rod groups) satisfies all regulatory and reactor design constraints, including governmental and customer-specified constraints. Additionally, the core design must be determined so as to optimize core cycle energy. Core cycle energy is the amount of energy that a reactor core generates before the core needs to be refreshed with new fuel elements, such as is done at an outage.
In the case of a BWR, for example, the number of potential bundle arrangements within the core and individual fuel element arrangements within a bundle may be in excess of several hundred factorial. From these many different possible configurations, only a small percentage of core designs may satisfy all applicable design constraints. Further, only a small percentage of these core designs, which do satisfy all applicable design constraints, are economical.
Traditionally, core design determinations have been made on a trial and error basis. Specifically, and based on only the past experience of the engineer or designer, in designing a core design an initial core design was identified. The initially identified design was then simulated in a computer. If a particular design constraint was not satisfied, then the arrangement was modified and another computer simulation was run. Many weeks of resources typically were required before an appropriate core design was identified using the above-described procedure.
For example, a current process being used is a stand-alone manual design process that requires a designer to repeatedly enter reactor plant specific operational parameters into an ASCII text file, which is an input file. Data entered into the input file includes blade notch positions of control blades (if the evaluated reactor is a boiling water reactor (BWR)), core flow, core exposure (e.g., the amount of burn in a core energy cycle, measured in mega-watt days per short time (MWD/st), etc.
A Nuclear Regulatory Commission (NRC) licensed core, simulation program reads the resulting input file and outputs the results of the simulation to a text or binary file. A designer then evaluates the simulation output to determine if the design criteria have been met, and also to verify that no violations of margins to thermal limits have occurred. Failure to meet design criteria (i.e., violations of one or more limits) require a manual designer modification to the input file. Specifically, the designer would manually change one or more operation parameter and rerun the core simulation program. This process is repeated until a satisfactory core loading pattern is achieved.
This process is extremely time consuming. The required ASCII text files are laborious to construct, and often are error prone. The files are fixed-format and extremely long, sometimes exceeding five thousand or more lines of code. A single error in the file results in a crash of the simulator, or worse, results in a mildly errant result that may be hard to initially detect, but will profligate with time and iterations to perhaps reduce core cycle energy when placed in an actual operating nuclear reactor core.
Further, no assistance is provided via the manual iterative process in order to guide a designer toward a more favorable core loading pattern solution. In the current process, the responsible designer or engineer's experience and intuition are the sole means of determining a core design solution.